Effect of microcracking on the deformation of ice

We review the findings of approximately 60 years of in situ and remote sensing studies of glacier crevasses, as well as the three broad classes of numerical models now employed to simulate crevasse fracture. The relatively new insight that mixed-mode fracture in local stress equilibrium, rather than downstream advection alone, can introduce nontrivial curvature to crevasse geometry may merit the reinterpretation of some key historical observation studies. In the past three decades, there have been tremendous advances in the spatial resolution of satellite imagery, as well as fully automated algorithms capable of tracking crevasse displacements between repeat images. Despite considerable advances in developing fully transient three-dimensional ice flow models over the past two decades, both the zero stress and linear elastic fracture mechanics crevasse models have remained fundamentally unchanged over this time. In the past decade, however, multidimensional and transient formulations of the continuum damage mechanics approach to simulating ice fracture have emerged. The combination of employing damage mechanics to represent slow upstream deterioration of ice strength and fracture mechanics to represent rapid failure at downstream termini holds promise for implementation in large-scale ice sheet models. Finally, given the broad interest in the sea level rise implications of recent and future cryospheric change, we provide a synthesis of 10 mechanisms by which crevasses can influence glacier mass balance. Field ObservationsBy virtue of providing relatively easy access to a glacier's interior, crevasses can be an asset to observational glaciologists, permitting, for example, the efficient examination of glacier stratigraphy. Annual accumulation

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“…Early applications to the material behavior of ice were presented by Jordaan et al . [] and Xiao and Jordaan []. Subsequently, Pralong et al .…”

Section: Crevasse Modelsmentioning

confidence: 99%

Glacier crevasses: Observations, models, and mass balance implications

Colgan

Rajaram

Abdalati

et al. 2016

Reviews of Geophysics

185

199

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“…In earlier tests, Jordaan and others (1992) examined the creep response of intact (i.e. undamaged) and damaged ice (to 2% total strain at 10 −4 s −1 ) under uniaxial conditions.…”

Section: Resultsmentioning

confidence: 99%

“…Shear stresses are the predominant cause of damage, but concurrent hydrostatic pressure must also be taken into account. Previous experimental work by the present research group on ice that has undergone changes to its microstructure (Stone and others, 1989; Jordaan and others, 1992) was focussed on the effects of microcracking on the stress-strain response of ice. The main effect of microstructural change was a reduction in elastic modulus and a large enhancement in the creep rate.…”

Section: Introductionmentioning

confidence: 99%

Experiments on the damage process in ice under compressive states of stress

et al. 1997

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During ice-structure interaction, ice will fail in a brittle manner dominated by two processes. The first corresponds to the formation of macrocracks and the consequent spalling-off of large ice pieces. The second includes an intense shear-damage process in zones, termed critical zones, where high pressures are transmitted to the structure. The shear-damage process results in microstructural changes including microcrack formation and recrystallization. A range of tests on laboratory-prepared granular ice have been conducted to determine the fundamental behaviour of ice under various stress states and stress history, particularly as it relates to changes in microstructure. The test series was designed to study three aspects: the intrinsic creep properties of intact, undamaged ice; the enhancement of creep and changes in microstructure due to damage; and the effects of different stress paths. Tests on intact ice with triaxial confining pressures and low deviatoric stresses, aimed at defining the intrinsic creep response in the absence of microcracking, showed that an accelerated creep rate occurred at relatively low deviatoric stresses. Hence, a minimum Creep rate occurred under these conditions. Recrystallization to a smaller grain-size and void formation were observed. Ice damaged uniaxially and triaxially prior to testing showed enhancement of creep under both uniaxial and triaxial loading conditions Creep rates in triaxially damaged ice were found to be non-linear with high deviatoric stresses, corresponding to a power-law dependence of creep rate. Uniaxially damaged specimens contained microcracks parallel to the stressed direction which tended to close under triaxial confinement. Damage under triaxial conditions at low confining pressures produced small recrystallized grains near zones of microcracking. At high confining pressures, a fine-grained recrystallized structure with no apparent cracking was observed uniformly across the specimen. The recrystallization process contributes significantly to the enhanced creep rates found in damaged specimens.

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“…Previous experimental work has examined the effects of damage on the mechanical behavior of ice (Stone and others, 1989; Jordaan and others, 1992). Results from triaxial testing by Stone and others (1997) have shown that enhanced creep rates occur in ice that has been subjected to prior damage as a consequence of a small axial strain applied at a rate of 10 −4 s −1 .…”

Section: Introductionmentioning

confidence: 99%

“…Previous investigations of damage in ice have focused on microcracking, under both uniaxial and triaxial conditions (Kuehn and others, 1988; Stone and others, 1989; Jordaan and others, 1992; Jordaan and Xiao, 1993; Rist and Murrell, 1994). Stone and others (1997) have shown that dynamic re-crystallization is also a mechanism of softening at higher stress levels, leading to greatly enhanced creep rates.…”

Section: Introductionmentioning

confidence: 99%

Microstructural change in ice: I. Constant-deformation-rate tests under triaxial stress conditions

et al. 1999

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Extensive damage to ice occurs during ice structure interaction by microcracking, recrystallization and melting. The objective of this work was to investigate this damage process under confined-stress conditions believed to be associated with impact zones that occur during ice–structure interaction. “Damage” refers to microstructural modification that causes deterioration of the mechanical properties. Prior experimental work has shown that a small amount of deformation causes permanent damage in ice, leading to enhanced creep rates during subsequent loading. To investigate this softening, freshwater granular ice was deformed under moderate confinement (20 MPa) at –10°C, at two rates which bracket ductile and brittle behavior (10−2 s−1 and 10−4 s−1). Samples were deformed to different levels of axial strain up to 28.8%. Thin sections were examined to assess the progressive changes in microstructure.Both grain-boundary and intra-granular cracking began at strains corresponding to the peak stress (1–2%) for tests at both strain rates. The peak stresses were 23.4 MPa for the tests at 10−2 s−1 and 9.8 MPa for the tests at 10−4 s−1. At strains of > 1–2%, dense clusters of intra-granular cracks began to develop in the samples tested at the higher rate. At the lower rate, dynamic recrystallization was apparently the dominant deformation mechanism beyond the peak stress. The average grain-size decreased strongly during the first few per cent strain and then maintained a relatively stable value.

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Effect of microcracking on the deformation of ice

Cited by 16 publications

References 8 publications

Glacier crevasses: Observations, models, and mass balance implications

Glacier crevasses: Observations, models, and mass balance implications

Experiments on the damage process in ice under compressive states of stress

Microstructural change in ice: I. Constant-deformation-rate tests under triaxial stress conditions

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